This invention relates to an improved covering fablic named "molton" to form the outer surface of a damping roller of a printing machine for supplying water to a plate cylinder. More particulaly, this invention relates to a covering fablic for a damping roller of a printing machine prepared by knitting fibers shrinkable by oneself or by water as annex yarns and hydrophilic fibers as ground yarns and as pile yarns.
In offset printing it is necessary to supply water to the plate cylinder of an offset printing machine, and this water supply is an important factor in determining the finishing of prints. Hitherto, the most popular damping roller covering fabrics, used to supply water to the plate cylinder, were prepared by fabricating a cloth made by knitting or weaving cotton into a cylindrical shape, mounting it onto a damping roller or a water ductor roller, and stretching and binding it by pulling the opposite ends of the cylindrically shaped cloth before use.
However, this conventional technique is accompanied with difficulties in that the covering fabric is apt to be loosened by the centrifugal force during rotary use of it, the supply of water to the plate cylinder becomes uneven due to uneven stitching, and cutting takes place which results in reducing the printing precisensess.
The printing operation must, therefore, be interrupted frequently to replace the covering fabric with a fresh one or to rebind the old one, which results in reducing efficiency of the printing operation. Also, the replacing operation of the covering fabric is quite troublesome and requires expensive skilled labor.
So, to solve such a problem, the inventor of this invention had before invented this kind of water-shrinkable covering fabric that is disclosed in U.S. Pat. No. 3,926,701, issued on Dec. 16, 1975, and has been put to practical use. However, it is necessary for a water-shrinkable covering fabric of prior art to bind with wire or yarn in advance both of its ends on the shafts extending out from both sides of roller, because a covering fabric inserted on a roller shrinks in the direction of axis of roller as well as in the direction of circumference of roller when immersed in water. The shrinkage which occurs unevenly because of a friction between a covering fabric and the outer surface of roller makes the diameter of roller covered with a covering fabric unequal at the side of roller and its middle, making the outer surface of roller uneven. In the case of this roller, as a result of shrinkage, the supply of water, that is an important factor is determining the finishing of prints becomes uneven.